I 35M need help understanding my girlfriend's 21F playful behavior

So I (35M) have been seeing my gal (21F) for about 5 months; I know the age gap is significant but we talked about it at great length and I've expressed my concerns about the viability of having a functional future together. She's assured me that I am the man for her and I do love her; she's not the stereotypical GenZ that gets a bad wrap on Social. We get along well and carry ourselves with the same wisdom (we do live together; I just bought a new for us, my first home). She had a really rough upbringing, as did I, so we have our shared trauma from our shit parents and I know that shows up differently in our relationship for each of us. But we navigate it with patience and wisdom for the most part, it's not perfect but relationships are work and we both understand that. Anyway, as a 35yo man who's never married and doesn't have kids yet, my instinctive drive to breed and have a family has been at 100% since we've gotten together. We have great sex, when she let's me, but she's already at the "I'm tired, not tonight" stage and I'm starting to worry.

The thing is, she enjoys being playful throughout the day and she loves "pretending" to put her finger up my butt - it's constant. I play back and spank her and stuff, but does really want to do that with me in the bed? I want to her to be turned on, and I want to bring her pleasure, and if that means I let her inside her me then great, I'm happy to take it for the good of our union. I just don't know if it's what she subliminally trying to tell me. I would do anything for her, and I desire naughty foreplay, especially if it gets her turned up.